1. Field of the Invention
The present invention relates to an apparatus and method for determining the density of servo-tracks to be written to a disk drive during a servo-track writing operation.
2. Description of the Related Art
Disk drives permanently store information in the form of magnetic transitions written onto and read from one or more rigid disks. These transitions are written by a write element in generally concentric tracks on a storage medium that is formed on the disks. A servo system is provided in the disk drive that includes a plurality of servo sectors on the disks to enable a read element to access a particular track (i.e., to seek) and to remain on the track (i.e., to track-follow). One way to quantify the performance of a disk drive""s servo system is to measure its position error signal (xe2x80x9cPESxe2x80x9d), which indicates how much the read/write head strays from the centerline of the track. Servo information is written into servo sectors in a manufacturing process called servo-track writing.
Servo-track writing is performed by a device called a servo-track writer, into which a disk drive sub-assembly, called a head-disk assembly (HDA), is inserted. The HDA comprises a spindle motor, one or more disks rotatably mounted on the spindle motor, a head actuator, at least one read element, and at least one write element mounted on the head actuator for each disk. The servo-track writing process establishes the density of the tracks along a radius of the disk, known as the track density. Although the track density of a disk drive varies across the surface of a disk, track density is typically summarized as a single value of tracks per inch (xe2x80x9cTPIxe2x80x9d). Track density directly affects the capacity of the disk drive.
The track density is predetermined for a particular disk drive design to assure that HDAs made according to that disk drive design will have adequate track-following performance. However, because PES varies across the distribution of HDAs, some HDAs have much better PES than needed for the predetermined track density. These HDAs have PES margin that is currently not utilized.
One aspect of the present invention is a method for manufacturing a disk drive that comprises a head-disk assembly that has a disk with a storage medium. The head-disk assembly has a servo performance. A plurality of calibration tracks are written onto the storage medium at a calibration track density profile corresponding to a portion of a nominal track density profile. The servo performance of the head-disk assembly is measured at the calibration tracks. A selected track density profile is identified based on the measured servo performance of the head-disk assembly. A plurality of tracks are written to the storage medium of the disk at the selected track density profile.
Another aspect of the present invention is a servo-track writer that writes a plurality of calibration tracks on a storage medium of a head-disk assembly at a calibration stepping increment. The servo-track writer also writes a plurality of servo-tracks on the storage medium of the head-disk assembly at a selected stepping increment. The head-disk assembly comprises a read element, a write element, and an actuator. The head-disk assembly has a servo performance. The servo-track writer comprises a controller that processes a clock reference pattern to determine the circumferential location of the write element. The controller also directs the write element to write the servo-tracks to the storage medium. The servo-track writer also comprises a head positioner circuit and a servo performance measurement circuit. The servo performance measurement circuit measures an aspect of the servo performance of the head-disk assembly and identifies a selected stepping increment based thereon. The head positioner circuit comprises a positioning mechanism that imparts a step-wise movement to the actuator at a calibration stepping increment for writing the plurality of calibration tracks. The positioning mechanism imparts a step-wise movement to the actuator at the selected stepping increment for writing the plurality of servo-tracks to the storage medium.
Another aspect of the present invention is a disk drive that comprises a head-disk assembly that has a servo performance. The head disk assembly comprises an actuator, a read element, a write element, a spindle motor, and a disk that has a storage medium. The disk is mounted on the spindle motor. A plurality of calibration tracks are written onto the storage medium at a calibration track density corresponding to a portion of a nominal track density profile. The servo performance of the head-disk assembly is measured at the calibration tracks. A selected track density profile is identified based on the measured servo performance of the head-disk assembly. A plurality of servo-tracks are written to storage medium of the disk at the selected track density profile.